Sebastian
The presence of Sebastian (Julia in disguise) is an example of dramatic irony in the play, as nobody but Lucetta and the audience know that the page boy is really Proteus's former lover. Sebastian's service to Proteus generates some of Julia's most heart-wrenching expressions of love and loss, as she realizes she must woo another woman after Proteus abandons his love for her.
The Duke's Confrontation
When the Duke approaches Valentine and pretends to need helping wooing a lady, their confrontation is an example of dramatic irony. The audience knows that Proteus has already told the Duke every part of Valentine's plan, but because Proteus does not want his betrayal to be traced back to him, the Duke must find a way to expose Valentine without letting him know that his scheme has already been uncovered.
Valentine's Banishment
After Proteus secretly informs the Duke of Valentine's plan to escape with Silvia, the Duke banishes Valentine from Milan. Thus, for the majority of the play, Valentine believes that Proteus is still his best friend. It is not until the very end of the play, when Valentine hears Proteus threaten to rape Silvia, that he realizes how profoundly he has been betrayed by his friend.
Thurio and Valentine
The Duke of Milan refuses to let his daughter, Silvia, marry Valentine. Instead, he decides that she will marry Thurio, a wealthy nobleman, and that Valentine will be banished from Milan. Ironically, at the end of the play, Valentine threatens to kill Thurio if he marries Silvia, and this act of defiance impresses the Duke so thoroughly that he changes his mind and endorses his daughter's marriage to Valentine.
